1. Field of the Invention
The present invention relates to negative double lift dobby machines, and more particularly to double-lift machines wherein a heald frame is biased downwards by spring action, a rope suspending the heald frame is connected to a jack-lever, the center of a balance lever is pivotally attached to the jack-lever, the balance lever is provided with driving members corresponding to both ends of the balance lever, and both driving members reciprocate at opposite phases with each other so as to rock the balance lever through hook means and drive the jack-lever.
2. Description of the Prior Art
Examples of dobby machines in prior art are illustrated in FIGS. 4 and 5.
In FIG. 4, when a heald frame 102 is in the downward position, a rope 103 is supplied with tension corresponding to sum of tension of a spring 101 and weight of the heald frame 102, subtracted by upward combined force based on warp tension; when the heald frame 102 is in the upward position, the rope 103 is supplied with tension corresponding to sum of tension of the spring 101 increased because of the elongation during heald frame elevation, weight of the heald frame 102 and downward combined force based on warp tension. This tension in the rope 103 acts on a connecting portion 105 to a jack-lever 104 which is pivotally connected at a top end 106 to the center of a balance lever 107. When the heald frame 102 is in the downward position, upper and lower ends of the balance lever 107 push stoppers 110 and 111 fixed to the casing through arc-shaped contact pieces 108 and 109 attached to both ends, respectively.
On the contrary, when the heald frame 102 is in the upward position, as shown in dash-and-dot line of FIG. 4, at forward movement of an upper knife 112, for example, the contact piece 109 attached to the lower end of the balance lever 107 pushes the stopper 111 and a hook lever 114 pivotally attached to the upper end of the balance lever 107 is engaged to the upper knife 112 and opposes the tension in the rope 103. In this case, it is evident that both contact pressure of the contact piece with the stopper and reaction force at the engaging portion of the hook lever with the knife in the upward state of the heald frame 102 are greater than those in the downward state thereof.
However, problem of slip and contact variation in pushing contact portions during upward and downward motion of the heald frame 102 is rather serious than amount of the reaction force therein. The contact pieces 108 and 109 are arc-shaped, but the balance lever 107 is pivotally attached to the jack-lever 104 which rocks. During rocking motion of the balance lever 107 involved in the motion of the jack-lever 104, the contact pieces 108 and 109 push the stopper 110 and 111 not at simple rolling contact but at sliding state. Moreover, since the contact is effected at line contact, the load per unit area becomes larger, resulting in abrasion at contact portions.
The knives 112 and 113 are heald substantially in the horizontal direction, but they are pivotally attached to upper and lower ends of a rocking lever 116 supported at the center. Accordingly, motion of the knives 112, 113 and that of pivotal portion of the hook lever 114, 115 follow respective circular arcs different in radius lenght. Therefore variation of contact state occurs at engaging portions between hooks of the hook levers 114, 115 and the knives 112, 113. This also causes abrasion in contact portions.
As above described, the dobby machine of this type has a disadvantage that abrasion of working parts causes rapid reduction of function.
In the dobby machine of this type, control rods 117 and 118 controlling the hook levers 114 and 115 or the like are interposed between the knives and the balance lever. In order to obviate interfere between parts, therefore, distance between the knives and the balance lever is taken large thereby the hook lever become longer than required for working. This obstructs the high-speed operation and requires the larger installation area.
FIG. 5 shows another example of prior art. In this figure, the spring 101, the heald frame 102, the rope 103, the jack lever 104 or the like are constituted similarly to FIG. 4. The center of a balance lever 120 is pivotally attached at 119 to the jack lever 104, and hook levers 121 and 122 are pivotally attached to both ends of the balance lever 120. A rocking lever 123 is provided with rocking shaft concentric to the balance lever pivotal shaft 119. Driving members 124 and 125 fixed to both ends of the rocking lever 123 are opposite to base portions of the hook levers 121 and 122, respectively. The driving members 124 and 125 push base portions of the hook lever 121 and 122, when the heald frame 102 is in the downward position. Stopping hook levers 126 and 127 are pivotally attached to shafts fixed on the casing. Command arms 128 and 129 are pivotally mounted in concentric relation and connected with each other through a spring. The command arms 128 and 129 work responding to pegs on a peg card. For example, the rocking lever 123 is rotated counterclockwise and the hook lever 122 is engaged with the stopping hook lever 127. If the rocking lever 123 is rotated clockwise in this state, the balance lever 120 is rotated clockwise about the pivotal shaft to the hook lever 122 and the jack-lever 104 is also rotated clockwise thereby the heald frame 102 rises.
As the dobby machine is constituted as above described, when the hook lever 121, 122 are not engaged with the stopping hook levers 126, 127 and the heald frame is in the downward position the balance lever 120 rocks integral with the rocking lever 123 about the pivotal portion 119 to the jack-lever 104. In this state, tension of the rope 103 produces reaction force to the pivotal portion 119 through connecting portion. If one of a plurality of heald frames 102 is not used corresponding to textile pattern, the jack-lever 104 and the balance lever 120 corresponding to the unused heald frame 102 are rocked under the load at the pivotal portion. Accordingly, abrasion may occur in these jack lever 104 and balance lever 120 in similar grade to those corresponding to the used heald frame 102.
Accordingly, both examples of conventional negative dobby machines using a balance lever have disadvantages.